A passive optical interface element, used in optical systems in which three lengths of monomodal optical fiber are connected to the optical interface element, is known in literature and available on the market. An interface assembly incorporating such an interface element utilizes connectors to connect various active components and assembly elements to the monomodal optical fibers which are in turn used to interconnect the various interface assembly elements and active components together optically.
As is well known by any person skilled in the art, the lengths of monomodal optical fibers used to connect the various interface assembly elements and active components together in an optical system should have a length of not less than 60-100 cm. and cannot be curved or bent very tightly. This is because monomodal optical fibers having a length of less than about 50-60 cm. become multimodal. Additionally when the bending radius of an optical fiber becomes too tight, the optical losses become excessive. Consequently the passive optical interface assembly has significant dimensions due to the additive, dimensions of the connectors, the active components, the passive interface elements and the lengths of optical fiber connecting the active components (receiver and laser) to the passive elements.
The above described transceiver system of known type is therefore very bulky and expensive. Additionally, the correct positioning of all lengths of optical fiber with respect of the active components and the passive elements must be performed manually by qualified staff and requires rather long alignment times with a consequent low yield in the production process.
U.S. Pat. No. 4,592,619 discloses an optical transceiver module for
a light transmitter and a light receiver to a single multimode optical fiber. This device uses two separated and different conventional lenses, namely a spherical lens and a planoconvex lens together with a planar filter interposed between them. The paths of the optical beams within the housing are through the air or other medium the housing is filled with.
Such known couples have the disadvantage of requiring a fine and difficult three-dimensional positioning of the members, as well as of requiring the physical means to accomplish this three dimensional positioning. The cost thereof is further raised by the use of two different kind of lenses in the optical system. Such device is subject to misalignment losses due for example to vibrations, changes of mechanical dimensions due to temperature changes, and changes of the refractive index of the medium within the housing (which may be caused, for example, by temperature changes or sealing defects of the housing).